(1) Field of the Invention
This invention relates to a thread tension adjusting apparatus, used in a sewing machine, for adjusting tension of a supplied thread by adjusting a thread holding force, the apparatus being provided on a thread supply path running from a thread source to a thread processing section such as a needle and a looper, especially to a thread tension adjusting apparatus for adjusting thread tension using a piezoelectric actuator.
(2) Description of the Prior Art
Thread tension adjustment for a sewing machine is done in two ways: 1) by continuously applying tension to the thread and 2) by applying tension to the thread for a specified period for each stitch. In the latter case, the thread tension should be changed at a high speed, which requires a thread tension adjusting apparatus having a high-speed responsibility.
For obtaining such a high-speed responsibility, a thread tension adjusting apparatus equipped with a piezoelectric actuator has been developed as disclosed in Japanese Utility Model Publication Kokai No. 61-180683 and Japanese Patent Publication Kokai No. 1-192391.
In such an apparatus, although the actuator possesses a high-speed responsibility, a thread holding member cannot hold the thread at a desirable timing for each stitch due to the inertia force caused by the weight of the member itself.